The present invention relates to an improved sliding closure unit having an easily replaceable lower stationary refractory plate. More particularly, the present invention is directed to an improved sliding closure unit for controlling the discharge of molten metal from a metallurgical vessel and being of the type including an upper or bottom stationary refractory plate to be mounted on the metallurgical vessel with a discharge opening aligned with a discharge nozzle of the metallurgical vessel, a movable refractory plate urged into sealing contact against the upper stationary refractory plate and having a discharge opening, sliding means for moving the movable refractory plate in a direction of movement between an open position with the discharge openings of the movable refractory plate and the upper stationary refractory plate in alignment and a closed position with the discharge openings out of alignment, a lower or locking stationary refractory plate mounted beneath the movable refractory plate, and tensioning means for pressing the lower stationary refractory plate against the movable refractory plate. The lower stationary refractory plate preferably has mounted thereon a refractory pouring tube.
A sliding closure unit of this general type is disclosed in DE-OS No. 22 19 064 and includes sliding means, movable back and forth in a direction of movement by a pressure cylinder, comprising an impact member connected to a piston rod of the pressure cylinder. Traction rods are attached to the impact member and extend laterally along the movable refractory plate. A traction member is attached to ends of the traction rods and connects the rods. When a movable refractory plate is to be replaced, a new movable refractory plate is positioned between the movable refractory plate already in use and the extended traction member and then thrust by the pressure cylinder via the traction member into the position of the worn plate previously in use. This newly positioned movable refractory plate is pressed against a bottom or upper stationary refractory plate by spring-loaded levers which are laterally positioned and which pivot about fixed axes. A holding or lower stationary refractory plate, having the refractory pouring tube connected thereto, likewise is pressed against the movable refractory plate by rocker or pivotally mounted levers. When the lower stationary refractory plate, together with the refractory pouring tube, is to be replaced, a new unit is positioned between the extended traction member and the lower stationary refractory plate already in use, in a manner similar to that described above regarding replacement of the movable refractory plate. This new lower stationary refractory plate is pressed against the used lower stationary refractory plate by the traction member by actuating the pressure cylinder until the new lower stationary refractory plate assumes the position of the previously used one.
However, a disadvantage of this type of replacement system is the fact that the refractory pouring tube and the locking or lower stationary refractory plate can be replaced only by operation of the pressure cylinder. Furthermore, this arrangement requires special holding structures for receiving and moving the lower stationary refractory plate, as well as detachable blocking structures to prevent unintended shifting thereof.